1. Field of the Invention
The present invention relates to a range change device of a shift-by-wire system which changes a shift range of an automatic transmission of a vehicle through an electric signal.
2. Description of the Related Art
In recent years, a shift-by-wire system which changes a shift range of an automatic transmission of a vehicle through an electric signal, in accordance with instructions of a driver of the vehicle, has been applied to a vehicle control. It is necessary for a vehicle to be reliably stopped and towed even when failure occurs due to some factor. In the case of a vehicle of the related art, in which a shift-by-wire system is not used, a shift range of an automatic transmission is changed to a P range or a parking brake is operated, in such a manner that the vehicle can be stopped. Furthermore, the shift range of the automatic transmission is changed from the P range to other ranges, in such a manner that it is also possible to easily perform towing of the vehicle.
However, in a case of a vehicle to which a shift-by-wire system is applied, a shift range of an automatic transmission is electrically changed. Accordingly, when failure, such as exhaustion of a battery or disconnection in wiring, occurs in a power source or a power supply system, it is difficult to change the shift range of the automatic transmission. Thus, even the vehicle including the shift-by-wire system requires a range change device which can change the shift range of the automatic transmission when failure occurs in the vehicle due to some factor.
In a shift-by-wire device (in other words, an SBW device) disclosed in JP-2008-180250A, a capacitor is provided to store power supplied to range control means, as a method of changing a shift range of an automatic transmission when failure occurs in a power supply system. Thus, even when failure occurs in a battery or a power supply system, an actuator of the SBW device can allow the shift range of the automatic transmission to be changed to the “P range” at least once, using the power stored in the capacitor. As a result, the vehicle is safely and reliably stopped.
Furthermore, a lever is operated, in such a manner that the shift range of the automatic transmission is manually released from a “P range”. As a result, the vehicle in a parked state can be easily moved by, for example, traction.
The SBW device of the related art is a countermeasure in which it is assumed that, when power is not supplied due to, for example, failure in the power supply system, the actuator changes the shift range to the P range using power stored in the capacitor. However, when failure occurs due to a voltage reduction in the power source, the actuator of the SBW device of the related art does not normally operate, and thus there is a problem in that the shift range cannot be changed.